Although scientists have long known that plant roots can communicate with plant shoots, the exact mechanism behind this process has been hazy. Now, a team of scientists from the University of Oxford has shed light on this process, which is essential for the coordination of plant shoots absorbing carbon from the air and plant roots extracting nutrients from the soil in order to optimize the metabolism and growth of the whole plant.
"Our paper shows that communication is achieved via movement of an agent from shoot to root. This agent is a protein known as HY5, a kind of protein known as a 'transcription factor' that can activate, or 'switch on', genes," Nick Harberd, who participated in the research, said in a press release. "HY5 was already known to control rates of photosynthesis (CO2 capture) in the shoot. Our work shows that HY5 acts as an agent of communication between shoot and root by moving through the phloem vessels (part of the plant vascular system)."
The results show that HY5 makes its way from the shoot to the root, where it then activates numerous genes in the root cells, including those that enable the extraction of nitrate from the soil. However, this activation is dependent on sugars, a measure of the carbon dioxide capture achieved by the shoots, which also travel from the shoot to the root. Ultimately, HY5 and sugars move from the shoot to the root in order to increase root nitrate uptake.
"In terms of fundamental science, this new knowledge significantly advances our understanding of how plant shoots and roots communicate with one another, and especially how that communication coordinates whole-plant growth and metabolism," Harberd said. "This is just the beginning of what is likely to become a major new area in fundamental plant biology."
The new findings could help breeders target HY5 in order to improve nitrate uptake from the soil and bolster plant growth, as well as reduce the ecological damage of fertilizer run-off from fields.
The findings were published in the Feb. 11 issue of Current Biology.
